In bulk polymerization (also called mass polymerization), the reaction medium is typically solventless; i.e., the monomer may be polymerized in the absence or substantial absence of any solvent, and in effect, the monomer itself may act as a diluent. Since bulk polymerization involves mainly monomer and catalyst, there is reduced potential for contamination and the product separation can be simplified. Economic advantages include lower capital cost for new plant capacity, lower energy cost to operate, and fewer people to operate may be realized. The solventless feature can also provide environmental advantages with reduced emissions and wastewater pollution.
Nonetheless, bulk polymerization can require careful temperature control, and there may be a need for strong and elaborate stirring equipment since the viscosity of the polymerization system can become very high. In the absence of added diluent, the cement viscosity and exotherm effects can make temperature control very difficult. Also, cis-1,4-polybutadiene is insoluble in 1,3-butadiene monomer at elevated temperatures.
For these reasons, bulk polymerization processes have not proven to be commercially successful. Since the advantages associated with bulk systems are very attractive, there is a need to improve the polymerization systems that are conducted in bulk.